This invention relates to stop mechanisms; and more particularly to a soft-stop mechanism for use on the read/write head carriage of a rotating disk storage system. Even more particularly, this invention relates to a soft-stop mechanism that uses a preloaded elastomeric tube; is self centering; is easily adjustable; eliminates the need for bonding agents during manufacture; and prevents movement of the carriage, other than in its normal direction of movement, while stopping the carriage.
In a rotating disk storage system, a carriage mechanism moves the read/write heads radially over the surface of the disk. The radial movement of the carriage is controlled by a servo controller that positions the heads over the desired track in order to perform the read or write function. The overall movement of the carriage, in either direction, during normal operation is less than the total mechanical movement possible for the carriage.
Unfortunately, it is possible for an electrical failure, in the servo controller or related circuitry to cause the carriage to move at full speed in either direction of travel. If this occurs, and some mechanism is not provided to stop the carriage during such a failure, the carriage will "crash" into the mechanical limit of its travel. Such a crash may not only seriously damage the carriage mechanism, it may also cause the read/write heads, which are positioned very close to the disk surface (on the order of a micrometer for a magnetic disk system, and on the order of a millimeter for an optical disk system) to strike the disk surface, thereby causing damage to both the heads and the disk surface.
Although such electrical failures seldom happen, it is a universal practice in the art to provide a soft stop at each end of the carriage travel. A soft stop can be defined as a mechanism which cushions the carriage at the end of its mechanical travel, bringing it to a stop without imparting a shock sufficient to cause damage to the carriage, heads, or disk surface. Further, a soft stop is sometimes provided on each side of the carriage, at both ends of travel, to prevent the carriage from twisting as it is stopped.
In addition to a soft stop, it is also a universal practice to provide a hard stop at each end of travel. A hard stop can be defined as a mechanical stop that the carriage will hit if the cushioning effect of the soft stop is not sufficient to stop the movement of the carriage. A carriage seldom hits the hard stop; but if it does, proper design practice dictates that both the soft and hard stops prevent a damaging shock from being transmitted to the carriage. As in the case for soft stops, a hard stop is usually provided on each side of the carriage, at each end of travel.
In the prior art, soft stops typically consist of an elastomeric pad or a helical spring upon which a mechanical section of the carriage impinges. Hard stops are typically a fixed piece of metal upon which a mechanical section of the carriage impinges after compressing the soft stop.
Both elastomeric pads and helical springs, when used as soft stops, have disadvantages. Elastomeric pads are typically bonded in place during manufacture with a bonding agent. This process is not only time consuming (a sufficient curing time must elapse for the bonding agent to cure) but it is not totally reliable. That is, the pad may fall off some time after installation because of a poor bonding technique. Since the pad is in the interior of the disk system, its absence may never be noticed until a failure causes a catastrophic crash.
Helical springs can be bulky and are generally constrained so that they compress in the direction of motion of the carriage. If they are not constrained, they may bow out of the direction of travel and not provide the anticipated compression force. If they are constrained, the constraining mechanism may jam the spring such that it does not return to its relaxed position after use, making it inoperative for the next crash which might occur.
Disadvantageously, neither of the prior art soft stop methods discussed above prevent the carriage from leaving its normal line of motion while a soft stop is occurring. Hence, during a soft stop it is also possible for the carriage to move in a direction perpendicular to the disk surface, thereby causing damage to both the heads and the disk. Also, it is difficult in the prior art to adjust the hard stops so that they stop the carriage only after the full compression of the soft stop has occurred.
Thus, there is a need in the art for an improved soft-stop mechanism. The present invention addresses that need.